The present invention relates to electrical connectors and, more particularly, to electrical connectors for interconnecting electrical circuit members such as printed circuit boards, circuit modules, or the like, which may be used in information handling system (computer) or telecommunications environments.
The current trend in design for connectors utilized in high speed electronic systems is to provide high electrical performance, high density and highly reliable connections between various circuit devices, which form important parts of those systems. The system may be a computer, a telecommunications network device, a handheld xe2x80x9cpersonal digital assistantxe2x80x9d, medical equipment, or any other electronic equipment.
One way high electrical performance is manifested is in improved signal integrity. This can be accomplished by providing the interconnections with shielding that helps them to more closely match a desired system impedance. High reliability for such connections is essential due to potential end product failure, should vital misconnections of these devices occur. Further, to assure effective repair, upgrade, and/or replacement of various components of the system (e.g., connectors, cards, chips, boards, modules, etc.), it is also highly desirable that, within the final product, such connections be separable and reconnectable in the field. Such a capability is also desirable during the manufacturing process for such products in order to facilitate testing, for example.
A land grid array (LGA) is an example of such a connection in which each of two primarily parallel circuit elements to be connected has a plurality of contact points, arranged in a linear or two-dimensional array. An array of interconnection elements, known as an interposer, is placed between the two arrays to be connected, and provides the electrical connection between the contact points or pads.
LGA interposers described in the prior art are implemented in many different ways. Many of these were described and compared in U.S. patent application Ser. No. 09/645,860, U.S. Pat. No. 6,312,266. Compared to the prior art, the inventive LGA carriers described in that referenced patent application significantly improve the reliability of LGA carriers. But to improve the electrical performance, further invention is necessary.
One way to improve electrical performance of LGA connectors is to provide electrical shielding for each individual contact member and to emulate a coaxial cable by terminating each shield separately. This is impractical to implement, especially when space is limited and low costs are important. An alternative to this is to provide shielding of contact members where the shielding is terminated to the surrounding structures en masse. This provides a wide variety of alternatives that vary in complexity. The technique can provide a proper amount of shielding to one or more reference voltage levels of the surrounding structures in a more cost effective fashion.
At first viewing some of the elements of U.S. Pat. No. 5,599,193, issued to Crotzer for RESILIENT ELECTRICAL INTERCONNECT, appear similar to those of various embodiments of the invention. However further study shows significant differences. The embodiment in FIGS. 1 and 2 of CROTZER describes an LGA connector with non-conductive elastomeric elements formed at the same time as is the elastomeric carrier for the elements, through a process such as molding. The elastomeric elements are selectively plated on their outer surface to create a plurality of conductive elements. Unfortunately, since the conductive elements rely on plating on the outside of the elastomer for conductivity, it would not be feasible to shield them electrically. Also, since the elastomeric elements are integrally formed with the carrier, it would be extremely difficult to repair a conductive element that has been damaged. Therefore, when damaged, the entire connector must be scrapped. Furthermore, since the carrier is composed of elastomer, its coefficient of thermal expansion (CTE) is substantially different from that of the surrounding structures.
The embodiment in FIGS. 4 and 5 of CROTZER illustrates an LGA connector with a rigid carrier that has openings with a shape complementary to the externally conductive elastomeric elements. Again, since the conductive elements rely on plating on the outside of the elastomer for conductivity, it would not be feasible to shield them electrically.
The individual cavities in the carriers for most prior art LGA connectors are cylindrical in shape and provide a minimal amount of retention of individual contact elements. Unfortunately, this makes the assembly and the proper engagement of the connector more difficult, since the individual contact elements may tend to fall out or shift vertically. Although a missing contact element will always result in an open circuit, an element shifted vertically may lead to permanent or intermittent problems maintaining uniform electrical and mechanical properties, thereby significantly reducing the reliability of the interconnection. The exception to this is the apparatus described in copending U.S. patent application Ser. No. 09/645,860.
A carrier that provides electrical shielding of the individual contact elements will result in LGA interposer connectors with improved electrical performance, constituting a significant advancement in the art.
It is, therefore, an object of the invention to enhance the electrical connector art.
It is another object of the invention to provide a carrier for land grid array connectors with improved electrical performance.
It is an additional object of the invention to provide a carrier for land grid array connectors with improved contact element retention.
It is an additional object of the invention to provide a carrier for land grid array connectors that results in a connector with improved manufacturability.
It is an additional object of the invention to provide a low profile carrier and land grid array connector combination.
It is an additional object of the invention to provide a carrier and land grid array connector combination that is reworkable if a contact member is damaged.
It is a still further object of the invention to provide a carrier for land grid array connectors that ensures uniform electrical and mechanical performance.
The present invention provides a carrier with electrical shielding of individual contact elements, resulting in LGA interposer connectors with improved electrical performance. The carrier includes a plurality of openings, each of which may contain an individual contact element. The openings may be plated with conductive material, and may also be commoned to one or more reference voltages (e.g., ground) present on at least one conductive layer of the carrier. The carrier may be as simple as a single unified structure with a conductive layer on one outer surface, or much more complex, comprising many layers of dielectric and conductive material. The carrier may also provide improved retention of the individual contact elements. Description of the process to assemble one embodiment of the carrier is also disclosed.